Hazardous Area Classification Questions

Hazardous Area Classification Questions

What is a hazardous area?

A hazardous area classification is one in which concentrations of flammable substances are present or can be expected to be present.

These concentrations are at a level which requires specific safety standards and precautions to be taken in the construction, installation and maintenance of all electrical equipment.

A “hazardous area” is defined as an area in which the atmosphere contains, or may contain in sufficient quantities, flammable or explosive gases, dusts or vapours. In such an atmosphere a fire or explosion is possible when three basic conditions are met. This is often referred to as the “hazardous area” or “combustion” triangle.

In order to protect installations from a potential explosion a method of analysing and classifying a potentially hazardous area is required.

The purpose of this is to ensure the correct selection and installation of equipment to ultimately prevent an explosion and to ensure safety of life.

The methods used to classify an installation can vary depending upon which part of the world it is located, but generally there are two main types of classification.

In countries that have adopted the IEC (International Electrotechnical Commission) philosophy this is referred to as Zoning whilst in North American installations are classified by Classes, Divisions and Groups to ascertain the level of safety required.

How Hazardous Area classified ?

The auto-ignition temperature of the hazardous material (temperature or “T” rating)

The likelihood of the hazard being present in flammable concentrations (zones)

Explain about Type of Hazard (Groups) ?

The type of hazard will be in the form of either a gas or vapour or a dust or fibre.

The classification of these hazardous is primarily divided into two groups depending on whether it is in a mining or above surface industry. These are defined below:

Group I – electrical equipment for use in mines and underground installations susceptible to firedamp Group II and Group III -electrical equipment for use in surface installations

Groups II & III are further sub-divided depending upon the hazard. Group II gases are grouped together based upon the amount of energy required to ignite the most explosive mixture of the gas with air. Group III dusts are subdivided according to the nature of the explosive atmosphere for which it is intended.

Explain about Auto Ignition Temperature or “T” Rating ?

The hazard level of the gases increases from gas group IIA to IIC with group IIC being the most severe.

Substances in this group can be ignited very easily with Hydrogen being the most at risk to ignition. The temperature class is based on the auto-ignition temperature of the gas.

If a hazardous is present the equipment used within the installation must be given an appropriate “T” classifi cation in order to maintain the integrity.

If that hazardous is, say, hydrogen, then all equipment used must meet the “T6” rating. This means that all equipment used must not have a surface temperature of greater than 85˚C.

Any equipment used that can generate a hotter surface temperature of greater than 85˚C must not be used as this will then increase the likelihood of an explosion by igniting the hydrogen in the atmosphere.

The Likelihood of the Hazard

The likelihood of the hazard being present in a concentration high enough to cause an ignition will vary from location to location.

For most installations this risk is dependant upon how long the hazard (gas, vapour, dust or fibre) is present.

In order to classify this danger an installation is divided into areas of risk depending upon the amount of time the hazardous is present. These areas are referred to as Zones.

For gases and vapours and dusts and fibres there are three zones:

classification of hazardous locations ?

Hazardous locations are classified into zones so as to facilitate the selection of the correct electrical apparatus and to ensure that the electrical design and installation meets the specified requirements to be used in different areas.

The zone classification is based on the likelihood and the duration of an explosive atmosphere.

The zone classification for gases is divided into three zones, namely Zone 0, Zone 1 and Zone 2 and for dusts Zone 20, Zone 21 and Zone 22.

Definition of hazardous area zones (AS/NZS 60079.10):

Zone 0

“Place in which an explosive atmosphere consisting of a mixture with air of flammable substance in the form of gas, vapour or mist is present continuously for long periods or frequently”

As per experts experience that a Zone 0 condition is rarely encountered and is limited mainly to confined spaces (such as the vapour space of closed process vessels, closed storage tanks and closed containers), although it can occur in larger rooms, such as chemical plants. From the Institute of Petroleum (IP 15) an exposure exceeding 1000 hours per year is often used.

Zone 1

“Place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally”

A Zone 1 classification usually includes locations where volatile flammable liquids or liquefied flammable gasses are transferred; gas generator rooms; inadequately ventilated pump rooms for flammable gases or for volatile flammable liquids; and most other locations where hazardous concentrations of flammable vapours or gases can occur in the course of normal operations. IP 15 stipulates between 10 hours and 1000.

Zone 2

“Place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only”

Generally, for an area to be classified as a Zone 2 location the following conditions shall normally be regarded as the minimum requirements for the area:

the area is so well ventilated that if an abnormal conditions arises, ignitable concentrations of the gas or vapour are rapidly dispersed; and

complete segregation from Zone 1 locations is ensured.

In this case an expose to flammable vapours or gases of less than 10 hours per annum is prescribed in IP 15.

Explain about Protection Concepts ?

There are varying types of equipment that can be used within these zones to ensure that the potential for an explosion is removed or greatly reduced.

This equipment must be designed and manufactured in accordance with particular construction parameters known as protection concepts.

Essentially these concepts fall under four main methods.

These methods are detailed below along with a brief description of some of the concepts:

Explain Ex i Intrinsic Safety ?

A protection concept in which the electrical energy within the equipment is restricted to a level which is below that what may cause an ignition or to limit the heating of the surface of the equipment.

There are two main sub types to Ex i protection, these being “ia” and “ib”.

Type “ia” protection allows for the occurrence of two faults during operation

Type “ib” protection allows for the occurrence of one fault during operation.

Explain Ex d Flameproof ?

The equipment that may cause an explosion is contained within an enclosure which can withstand the force of an explosion and prevent transmission to the outside hazardous atmosphere.

This method of protection also prevents the hazardous atmosphere from entering the enclosure and coming into contact with equipment.

Explain Ex m Encapsulation ?

A protection concept where by equipment that could potentially cause an ignition is encapsulated within a compound or resin so as to prevent contact with the explosive atmosphere.

The concept also limits the surface temperature of the equipment under normal operating conditions.

Explain Ex e Increased Safety ?

Precautions are applied to the installation to ensure increased security against the possibility of excessive temperatures and sparks from electrical equipment.

Equipment that normally causes sparks is excluded from use within this method of protection.

Explain Ex p Pressurised ?

One process ensures that the pressure inside an enclosure is sufficient to prevent the entrance of a flammable gas, vapour, dust, or fibre and prevent a possible ignition.

Another process maintains a constant flow of air (or an inert gas) to dilute to take away any potentially explosive atmosphere.

Explain Ex o Oil Immersion ?

All equipment that has the potential to arc and potentially cause an ignition is immersed in a protective liquid or oil.

The oil provides an insulating method to prevent ignition.

Explain Ex q Powder Filling ?

All equipment that has the potential to arc is contained within an enclosure filled with quartz or glass powder particles.

The powder filling prevents the possibility of an ignition.

Explain Ex n Non-Sparking ?

A type of protection where precautions are taken so that electrical equipment that has the potential to arc is not capable of igniting a surrounding explosive atmosphere.

This can be further categorized as follows:

Ex nA – Where components used in construction are non-sparking

Ex nC – Where components used in construction are non-incendive

Ex nR – Where components used are tightly enclosed to restrict the breathing and prevent ignition

Ex nL – Where components used in construction do not contain enough energy to cause an ignition

Explain Ex s Special ?

This method of protection, as its name indicates, has no specific parameters or construction rules.

In essence it is any method of protection which can provide a pre-determined level of safety to ensure that there is no potential for an ignition.

As such it does not fall under any specific protection method and may in fact be a combination of more than one.

Explain Ingress Protection ?

Another consideration in the protection of equipment in hazardous areas is the safeguarding against the ingress of solid foreign objects and water.

This is known as the degree of ingress protection and is commonly referred to as the IP Code.

The relevant standard for the degree of ingress protection is IEC 60529.

An overview of the IP code as defined in the standard is detailed below:

Explain Operational Temperatures ?

All equipment used within hazardous areas has an operational temperature band or limit. This is often referred to as the “Tamb” and defines the upper and lower ambient temperatures of which the equipment is approved for use in.

As defined in IEC 60079-0 the standard limits are – 20˚C to +40˚C. Where the operation temperatures of the equipment fall between these parameters no additional marking is required.

However, if they are outside these parameters than the specific temperatures need to be identified.

What are the Methods of Explosion Protection ?

Explain Marking of Hazardous Area Equipment ?

All equipment for use in hazardous areas should be marked as prescribed in 60079-0.

As a general rule this includes, where appropriate, such information as:

Explain Basic UL / CSA / NEMA Enclosure Types ?

Type 3 : An enclosure which is intended for outdoor use primarily to provide a degree of protection against windblown dust, rain, sleet and damage from external ice formation

Type 3R : An enclosure which is intended for outdoor use primarily to provide a degree of protection against falling rain and damage from external ice formation

Type 3S : An enclosure which is intended for outdoor use primarily to provide a degree of protection against rain, sleet, windblown dust, and to provide for operation of external mechanisms when ice laden

Type 4 : An enclosure which is intended for indoor or outdoor use primarily to provide a degree of protection against windblown rain and dust, splashing water, hose directed water and damage from external ice formation

Type 4X : An enclosure which is intended for indoor or outdoor use primarily to provide a degree of protection against corrosion, windblown rain and dust, splashing water, hose directed water and damage from external ice formation

Type 6 : An enclosure which is intended for indoor or outdoor use primarily to provide a degree of protection against falling dirt, hose directed water, the entry of water during occasional temporary submersion at a specified depth and damage from external ice formation.

Type 6P : An enclosure which is intended for indoor or outdoor use to primarily to provide a degree of protection against falling dirt, hose directed water and the entry of water during prolonged submersion at a specified depth and damage from external ice formation.

Why perform electrical equipment in hazardous areas inspections ?

Perhaps you have heard the expression ‘if it’s not broken don’t fix it’.

The same can be said for Electrical Equipment in Hazardous Areas (EEHA) inspections and there is often a great deal of resistance from engineering and production managers to perform electrical inspections which may involve the isolation certain equipment or partial plant shutdown.

It is a fact that if the electrical inspector lacks the necessary experience, the EEHA inspection could indeed do more harm than good, resulting in damage to electrical apparatus, tripping of electrical circuits or extended isolations.

For this reason only competent personnel should be employed for the purpose of performing EEHA inspections.

Using a competent electrical inspector will provide the owners or users of the plant with a condition assessment of the electrical installation in hazardous areas to ensure that it is maintained in a satisfactory condition.

It is also a requirement of AS/NZS 2381.1:2005 Section 4 that EEHA inspections be performed on a regular periodic basis or under continuous supervision by competent personnel.

Before embarking upon an inspection of electrical equipment within a hazardous area, the hazards associated with the flammable gas or vapour must be understood and the extent of the hazardous zone must be clearly defined. It is a fruitless exercise to begin an EEHA inspection without a clear definition of the hazardous zones.

Internationally, the classification of hazardous areas has traditionally been carried out by individuals representing the legal owners/users of the plant.

Often these persons lack expertise in hazardous areas classifications as well as the specific knowledge of the properties of the flammable materials. As a result, inconsistencies may exist in the limits of the hazardous zones.

However, in more recent times hazardous areas classification has tended to be carried out by professional multidisciplinary engineering consultancies specialising in hazardous locations classifications.

The electrical inspector performing the EEHA inspection should verify that the existing area classification remains correct and that there have been no changes to plant or processes that may affect the hazardous zones.

Does all electrical equipment for use in hazardous areas have to be submitted to a test house for certification?

No, electrical equipment in category 1, i.e. suitable for use in Zone 0,1 and 2 must be submitted to a test house (now known as a notified body) for EC Type Examination Certification.

This also applies to category 2 equipment (i.e. suitable for use in Zone 1 and 2) .

Equipment in category 3, i.e. suitable only for use in Zone 2 need only be subject to self certification by the manufacturer.

For all electrical equipment for use in hazardous areas, the manufacturer must issue an EC Declaration of Conformity with his product.

If an enclosure is marked II 2 GD and also EExd 11C T5 T100 IP 66, what is the meaning of the upper case and the lower case ‘d’s?

The upper case D is part of the ATEX labelling and indicates that the equipment is for use in areas where the explosion hazard is Dust (the G indicates Gas Hazard).

The lower case d indicates the method of Ex protection, in this case flameproof (d from the German Druckefest Kapselung meaning pressure proof enclosure).

I have an EExe electric motor which is labelled as T3, I understand this to mean that the temperature reached by any part of the motor will not be any greater than 200°C. Is this the case and do I need to consider ambient temperature effects?

This is true and if there is no ambient temperature range marked on the equipment then the T rating is based on a range of -20°C to +40°C.

Any other range must be marked on the label.

A flameproof EExd enclosure has a 32mm entry and we need to use it for a 20mm cable gland, is it permissible to use two reducers to achieve this?

No, EN 60079-1, the standard for flameproof equipment states that for any entry only one reducer can be used, also that reducers or adapters cannot be used at all with stopping plugs.